A known arrangement in a printing operation provides for the transfer of a portion of ink from a ribbon to result in a mark or image on a substrate sheet such as paper. Another known arrangement includes the use of paper wherein an impact element causes rupture of encapsulated material for marking the paper.
The process of electrophotographic printing includes charging a photoconductive member to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive surface is exposed to a modulated light beam, e.g., a laser beam, to discharge selected portions of the charged photoconductive surface to record the desired information thereon. In this way, an electrostatic latent image is recorded on the photoconductive surface. The latent image is developed by bringing developer material into contact therewith. Developer material may be comprised of toner particles adhering triboelectrically to carrier granules. The carrier granules may be magnetic, while the toner particles may or may not contain small amounts of magnetic media in a thermoplastic resin binder. The toner particles are electrostatically attracted from the carrier granules to the latent image, from whence they may be transferred to a substrate. Alternatively, single component or liquid carrier development could be used. Finally, the substrate may be subjected to heat and/or pressure to permanently affix the toner image to the substrate.
Also known are printing inks which contain magnetic particles wherein certain of the particles are transferred to the record media for encoding characters in a manner and fashion so as to be machine-readable in a subsequent operation. One of the best known uses for such encoding systems is in magnetic ink character recognition (MICR).
Electrophotographic printing in concert with the use of MICR technology has been particularly useful in the commercial banking industry by reproducing checks or financial documents with magnetic ink, i.e., by fusing magnetically loaded toner particles thereon. Each financial document has imprinted thereon encoded data in a MICR format. In addition, high speed processing of financial documents is simplified by imprinting magnetic ink bar codes in machine readable form thereon. The repeated processing of the financial documents and the high speed sorting thereof is greatly simplified by the reading of the encoded data by a MICR reader. Thus, encoded information on financial documents may be imprinted thereon xerographically with magnetic ink or toner. The information reproduced on the copy sheet with the magnetic particles may be subsequently read due to its magnetic and optical characteristics.
High speed electrophotographic printing machines have employed magnetic toner particles to develop the latent image. These toner particles have been subsequently transferred to the copy sheet and fused thereto. The resultant document may have variable or fixed magnetic data imprinted thereon in MICR format which is subsequently read by a MICR reader and processed. While the utilization of magnetically encoded information on documents reproduced with magnetic particles is well known, the cost of using magnetic toner as the only developer in a printer is substantial since every copy going through the printer uses up magnetic toner whether the subsequent copy is to be read by MICR reader or not.
Recently, the advent of thermal printing such as in facsimile machines has brought about the requirement for heating of extremely precise areas of the record media by use of relatively high currents. The intense heating of the localized areas causes transfer of ink from a ribbon onto the paper. Alternatively, the paper may be of the thermal type which includes materials which are responsive to the generated heat. The use of thermal printing is adaptable for MICR encoding of documents wherein magnetic particles are caused to be transferred onto the documents for machine reading of the characters. MICR character generation can involve the thermal transfer of a layer of magnetic material to the top of xerographically printed non-magnetic characters. Usually a magnetic tape comprising a substrate layer and a magnetic layer is heated. Upon contact with xerographically printed non-magnetic characters, the xerographically printed characters are softened by the heat, and the magnetic layer of the magnetic tape makes contact to adhere to the surface of the xerographically printed characters, thus magnetizing the characters. These characters can then be read by a machine. A preferred magnetic layer consists of approximately 60% acicular magnetite, 25% styrene, 7% chlorinated rubber, 6% carbon black and a small amount (&lt;1%) of plasticizer % by weight. These constituents are dispersed in a methyl ethyl ketone/toluene solvent and coated onto a 0.5 mil polyethylene terephthalate substrate to produce a 2 to 3 .mu.m thick layer after drying. A critical aspect of this formulation is to provide, within a single layer, a balance of adhesion forces such that the magnetic layer adheres to the toner, releases relatively easily from the PET and does not adhere to the paper.
The compositionally minor constituent (i.e. plasticizer) is the major component responsible for release and for determining the parameters of the tape's use. This fact has most likely been responsible for uncontrolled tape release characteristics which are manifested in high reject rate and process latitude variability.
U.S. Pat. No. 4,894,283 (Wehr) discloses a reusable thermal transfer ribbon with a thermal responsive coating thereon, for use in imaging or encoding characters to be machine read. The thermal transfer ribbon is comprised of three layers: (1) a base or substrate of thin, smooth, tissue- like paper or polyester type plastic or like material; (2) a layer or coating which includes a resin composition which may include polyethylene as an ingredient for use in providing a binding layer; and (3) a functional coating which is thermally activated and includes a nonmagnetic pigment or particles as an ingredient therein for use in imaging or encoding operations to enable machine, human, or reflectance reading of characters or other marks. The functional coating layer has a low cohesion level which allows the splitting of the functional coating during the printing operation in a manner to effect reusable or multiple use of the coating. The binding layer retains a portion of the split functional coating layer for reuse of the same portion of the ribbon.
U.S. Pat. No. 4,533,596 (Besselman) discloses a thermal magnetic transfer ribbon comprised of a tissue- or polyester-type resin to which is added a coating of a magnetic pigment and a resin, oil and wax mixture dispersed in a binder mix. The thermal magnetic ribbon or transfer medium is useful for encoding characters with a magnetic signal inducible ink, thus enabling the characters to be machine read.
U.S. Pat. No. 4,628,000 (Talvalkar et al.) discloses a thermal transfer formulation and medium comprised of a non-crystalline type adhesive-plasticizer or sucrose benzoate transfer agent dispersed in a diluent of ethyl alcohol or like solvent, and a coloring material or pigment. The formulation is coated on a ribbon substrate and provides for thermal printing on any receiving substrate having a substantially smooth surface.
One of the problems with the use of such an approach for MICR character generation is the frequent failure of the layer of magnetic material to readily separate from the substrate or backing layer. Consequently, documents are incompletely coded and cannot be properly machine read. Current toner film tapes for MICR give inconsistent performance and have variable latitudes.